Hylid or microhylid? No evidence for the occurrence of Trachycephalus mesophaeus (Anura, Hylidae) in Argentina

: A recent publication reported the Atlantic Forest endemic hylid Trachycephalus mesophaeus for the Chacoan ecoregion in Argentina. In this paper, we analyzed the voucher specimen and showed that it is a mis-identified specimen of the Asiatic microhylid Kaloula pulchra , a species commonly commercialized in the pet trade worldwide. Therefore, there is no evidence for the occurrence of T. mesophaeus in Argentina


THE NEW RECORD
Recently, Garcia-Marsà et al. (2020) reported a third species of Trachycephalus for Argentina, T. mesophaeus (Hensel, 1867), based on a single specimen (CFA-An-88; Scientific collection of Fundación de Historia Natural "Félix de Azara", amphibians; Ciudad de Buenos Aires, Argentina) informed as collected in Las Lomitas, province of Formosa, on October 3, 1986.Trachycephalus mesophaeus (Fig. 1 A-D) is a species known to occur in the Atlantic Forest of Southeastern and Eastern Brazil, from the states of Rio Grande do Sul to Pernambuco (e.g., Kwet et al., 2010;Haddad et al., 2013).Garcia-Marsà et al. (2020) identified the specimen explicitly based on color pattern, and, very likely (see below) on the fact that the specimen had a label identifying it as "Trachycephalus sp."The authors pondered the possibility that it could belong to "a still unknown population of the T. typhonius complex".However, as they concluded that the specimen showed "all morphological attributes of T. mesophaeus", they considered it to belong to this species.
Once they established the identification of the specimen, Garcia-Marsà et al. (2020) discussed possible reasons why T. mesophaeus has not been collected in recent years in Argentina.They considered that the species might be difficult to find, and as the Chacoan ecoregion is still poorly explored, they hypothesized that perhaps there are still healthy populations of T. mesophaeus in the Chacoan ecoregion.Alternatively, they discussed the possibility that the species has been locally extinct due to the substantial degradation of this ecoregion.Garcia-Marsà et al. (2020) also discussed the biogeographic significance of their finding of an Atlantic Forest-endemic species in the transition zone of the humid and dry portions of the Chacoan ecoregion.They considered that it was not uncommon, based on the evidence of past connections between the Atlantic Forest and the Amazon basin.They further suggested that their finding of a "relictual population" of T. mesophaeus could reflect the past, widespread distribution of gallery forests and associated fauna.
(2) Absence of a tympanic membrane (all species of Trachycephalus have a prominent tympanic membrane).(3) Foot and hand webbing basal or absent (all species of Trachycephalus have a considerable amount of foot webbing, and evident hand webbing).( 4) Non-expanded discs (all species of Trachycephalus have prominent discs in hands and feet).( 5) Absence of nuptial pads, despite being an adult male as revealed by the dark-colored vocal sac (present in all species of Trachycephalus).(6) Presence of an expanded, spade-like inner metatarsal tubercle (oval, not expanded in Trachycephalus).(7) Short hindlimbs (hindlimbs proportionally larger in Trachycephalus).Briefly: the specimen does not even remotely look like a hylid, nor is it similar to any other anuran species occurring in Argentina.
The study of the specimen CFA-An-88 (Fig. 1 E, F), besides corroborating all the characters that are evident in the published photographs, indicates that the specimen lacks maxillary and premaxillary teeth, and that it has two noticeable palatal folds.This combination of characters is only known to occur in anurans of the families Brevicipitidae and Microhylidae (Parker, 1934;Laurent, 1986).
From a purely taxonomic perspective, the specimen in question cannot be associated with Brevicipitidae as it lacks the very characteristic body shape and reduced mouth of the species in this family (see Channing & Rödel, 2019), thus pointing at the widely-distributed, diverse family Microhylidae (690 species; Frost, 2020).This family currently includes 13 (de Sá et al., 2012;Peloso et al. 2016) or 12 subfamilies (Tu et al. 2018;Streicher et al., 2020).Although there has been considerable progress in defining its major clades, recent discussions on the phylogenetic relationships of the family have barely referred to phenotypic evidence or taxonomic aspects.For this reason, the taxonomic identification of a microhylid without locality data could be challenging.Fortunately, this was not the case, as this specimen belongs to one of the microhylid species most commonly available in the pet trade: Kaloula pulchra Gray, 1831.
The distinctive dorsal pattern of the specimen, which consists of two light bands on the dorsolateral margins of the body, is also present in K. mediolineata, Uperodon anamalaiensis, and U. taprobanicus (Microhylinae) and Phrynomantis bifasciatus (Phrynomerinae).Kaloula pulchra differs from K. mediolineata, by the lack of a posterior middle-back stripe (Taylor, 1962), from the two species of Uperodon by its larger SVL and non-expanded discs in hands (Garg et al., 2018), and from Phrynomantis bifasciatus, for its lighter coloration, lack of ventral white blotches, larger forelimbs, longer toes, and dark gular pigmentation in adult males (Du Preez & Carruthers, 2009;Channing & Rödel, 2019).

LAyERS OF CONFUSION
Kaloula pulchra is a widely-distributed species, ranging from northern India to Vietnam, through Bangladesh, Myanmar, southern China, Thailand, and Laos, and south to Cambodia, Malaysia, Singapore, and Indonesia, and it has been introduced in the Philippines (Kuangyang et al., 2016;Pili et al., 2020;Frost, 2020).This species has been extensively commercialized in the pet trade, and imported to Argentina at least during the 1990s.
The specimen of Kaloula pulchra that Garcia-Marsà et al. (2020) misidentified as Trachycephalus mesophaeus is in a jar with a label indicating it as "Trachycephalus sp.Las Lomitas, Formosa.Col: José Soroca.03/10/1995."It is worth noting that there is no other specimen of this genus collected in Formosa housed in the collection of Fundación de Historia Natural Félix de Azara, although another species, T. typhonius has been collected in Las Lomitas (M.Duré, pers.comm.), and nearby localities in Formosa (e.g., Pozo del Tigre, MACN-He 54611; Colección Nacional de Herpetología, Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"-CONICET, Ciudad de Buenos Aires, Argentina).Furthermore, S. Bogan (pers.comm.)indicated that the specimen was accessioned as part of material sporadically donated by the collector.Clearly, at some point, there was a human error, the label was associated with the wrong specimen, and triggered a series of confusions that ended up with Garcia-Marsà et al. (2020) wrongly reporting T. mesophaeus for the first time in Argentina.Nevertheless, the fact that the manuscript reporting the "new" record, including illustrations of the remarkably misidentified specimen, found its way through the conventional filters of scientific publication, is worrisome.

Fig. 1 .
Fig. 1.A-B: Adult female of the hylid Trachycephalus mesophaeus LGE 10538 (Brazil: Rio Grande do Sul: Terra de Areia).C: Detail of nuptial pad, and D: gular region in ventral view of an adult male T. mesophaeus LGE 22305 (Brazil: São Paulo: Ubatuba).Vocal sacs are paired, lateral, and almost entirely restricted to the posttympanic region, with little subgular development, as evidenced by the lack of dark pigmentation in the area.E-F: Adult male of the microhylid Kaloula pulchra (CFA-An-88), the specimen identified as T. mesophaeus by Garcia-Marsà et al. (2020).G-H: Adult male Kaloula pulchra MACN-He 39171 (pet trade), a properly fixed and preserved specimen.Scale bars: 1 cm.Abbreviations not used in the main text: LGE: Laboratorio de Genética Evolutiva, Instituto de Biología Subtropical, Universidad Nacional de Misiones, Posadas, Misiones, Argentina.